Bradley, 23, passed his medical on Monday and will now be available to Gerard Houllier once he has obtained a work visa and international clearance.

The midfielder, who joined Borussia Monchengladbach in August 2008, impressed for United States at the World Cup finals last summer.

"I am really excited to be joining Villa," Bradley told the club's official website. "I am proud and thrilled and can't wait to get going now.

"Everyone can see that Villa is a big club, a fantastic club, with tradition and great supporters. Over the past few years Villa have made big strides and are trying to challenge at the very top of the Premier League. I am excited to be part of that and I am excited to be here.

"I want to play at the highest level and test myself in the biggest of games. Whether it's on Saturday against Fulham at Villa Park or the week after, I am excited to be here and ready to get going."

Villa manager Houllier said: "Michael is is a very hard-working midfielder who can score goals and is versatile. I saw him play four times at the World Cup in South Africa. I saw him once on TV but four times at the games for the national team, so in terms of scouting you cannot say the work has not been done. We're pleased that he is here at Aston Villa."